1. Field of Invention
This method of detection relates in general to anti-terrorism, and specifically to radioactive particle detection. The described invention will allow an existing building smoke/fire detection infrastructure to have enhanced usage for determining the presence of “dirty bomb” radioactive particle fallout. A “dirty bomb” is a low tech way of terrorist or adversarial groups to cause mass disruption by releasing low level radioactive particles into the air that are capable of causing public panic, contamination of buildings, real-estate, and sickness or death in humans and animals. The release can be abrupt and energetic, such as an explosive surrounded by low-level radioactive medical or nuclear waste, or slow and subtle by aerosolizing a low-level radioactive powder. By using real time readings of chamber values of commercially available ionization type smoke detectors in a new and novel way, one can indicate the presence of radioactive particles indicative of an accidental or intentional release of radioactive contaminates.
2. Background Description of Prior Art
In the case of smoke detection by an ionization smoke detector, a radioactive source producing ion pairs is used. They take advantage of the ion pairs created by ionizing radiation to develop a low, but measurable electrical current between two plates with a small voltage differential between them. This current is typically in the range of picoamps (10−12 Amps). Smoke particles entering the chamber (single or dual chamber design) decrease the current between the two plates and trigger the detector's alarm. Current fire alarm systems (or even the detector itself) have intelligent algorithms that will compensate for a detector chamber getting dirty over time and compensate for long term changes in chamber threshold. This will reduce the likelihood of a false alarm, and help to prevent an even worse scenario—no alarm when there is a real fire! All current methodologies rely on the fact that when smoke particles enter the ionization chamber, the small constant current that is present in the chamber will decrease to indicate the presence of smoke particles and indicate a fire. The amount of ionizing radiation, albeit small, will remain constant, only the current will decrease. The intent of this invention, is that when a “dirty bomb” is exploded or aerosolized radioactive particles are released into the atmosphere in what will most likely be a large metropolitan area (if terrorism is involved), a method of indication can be realized to warn building occupants that there is a quantity of harmful radioactive particles in the air. The software modification to the fire alarm panel will be the addition of a new alarm (possibly called “Radiation Alarm”, “Radioactive Particle Alarm”, or whatever else is decided) that will be sounded if one or more (preferably a group of) detectors indicate a rapid increase (several seconds to several minutes) in ionization chamber current, due to the presence of radioactive particles. The radiation from the particles will increase the limited but constant ionization produced by the detectors own ionization source. The alarm can cause specific events to be triggered from the fire panel; such as, closing outside air dampers, and turning off ventilation fans to minimize the amount of dispersion of radioactive particles that would be introduced into the building ventilation system.